The present invention relates to a sensing apparatus including an A/D conversion circuit for converting an analog sensing signal detected by a sensing circuit into digital data and a signal processing circuit for processing the digital data.
The Unexamined Patent Application No. 9-113310 or No. 10-281912 discloses a sensing apparatus comprising a selector for selectively outputting a pressure signal (i.e., sensor signal), a temperature signal, and a reference signal. Furthermore, the sensing apparatus comprises two oscillation circuits for detecting a time difference between two signals for A/D conversion based on the time A/D processing. In this case, the A/D conversion time is determined in accordance with a signal to be A/D converted, while a constant power source voltage is applied to the A/D conversion circuit.
However, according to such a conventional sensing apparatus, the circuit scale is enlarged due to provision of two oscillation circuits which are associated with capacitors and dividers.